Bioaccessibility of polycyclic aromatic hydrocarbons dependence on ingested plant species

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Abstract

Herbivores ingesting polycyclic aromatic hydrocarbon (PAH) contaminated
plants may be chronically exposed to PAHs through their diet. This PAH exposure, can result in toxic, mutagenic, carcinogenic, and teratogenic effects. However, little is known about how differences in morphology and physiology between plant species alters PAH environmental accumulation and release in the gastrointestinal tract after ingestion.
Bioaccessibility of PAHs was examined in six different sub-arctic plant species
[black spruce (Picea mariana); labrador tea (Ledum groenlandicum); bog birch (Betula glandulosa); green alder (Alnus crispa); water sedge (Carex aquatilis); and little-tree willow (Salix arbusculoides)] from a reference and PAH impacted site near Inuvik, Northwest Territories, Canada. Plants were digested using a simulator of the human upper digestive track and toxicity tested using the Aryl Hydrocarbon Receptor Assay (Ah assay).
Results show that there is a significant difference in bioaccessible PAH
concentration between the plant species tested (p < 0.05) in new growth. New growth of
green alder contained the highest, with 0.425 mg (SE = 0.1) benzo[a]pyrene (BaP) equivalent per gram of wet weight plant tissue, and black spruce contained the lowest BaP equivalent concentration of 0 mg BaP per gram of plant tissue. Of the plants species that exhibited bioaccessible PAH concentrations, those that were growing on the PAH contaminated site had accumulated up to 1.24x higher PAH concentrations. New growth plant tissue had on average a 69% and 38% greater bioaccessible PAH concentration than old growth for the reference and impacted site respectively.
Nominal additions of BaP with digested plant extracts revealed that black spruce, labrador tea, water sedge, and willow all contained endogenous Ah antagonists (p < 0.05). No correlation was elucidated between chemical and physical plant parameters such as % lipid content, cuticle thickness, and leaf surface area (p < 0.05). The lack of a correlation between the plant physical properties and BaP equivalent concentration may be a result of the antagonist effect some of the digested plant extracts had on the Ah assay. Understanding plant uptake and bioaccessibility of PAHs in ingested plant
matrices will aid in determining toxicological risk to herbivores inhabiting PAH contaminated sites.